1. Field of the Invention
The present invention relates to the technology for use in a moving object such as a vehicle and for obtaining a relative velocity vector to the moving object, and more specifically to a detecting and ranging apparatus and a detecting and ranging program product capable of obtaining a correct relative velocity vector in a simple calculation based on a relative distance or a relative velocity obtained by a plurality of detectors such as a radar.
2. Description of the Related Art
There has conventionally been an apparatus loaded into a vehicle such as an automobile for detecting the relative position and relative velocity to an object to be detected such as another vehicle with respect to the vehicle into which the apparatus is loaded.
For example, the following document discloses the technology of obtaining the difference of the virtual central point of a pivot on the road and the direction angle of an object to be detected by a single detector from a beam angle or a scan angle, and calculating the distance from the object to be detected.
There is also the disclosed technology of using a plurality of detectors.
For example, a radar capable of estimating all amounts of a relative distance, a relative velocity, and a direction with respect to an object to be detected.
Described below as a practical example of such a radar is a phase monopulse radar for estimating a distance and a velocity in the RMCW (frequency modulated continuous wave) system as a radar system for frequency modulating a transmission wave by a triangular wave etc., and estimating a direction in a phase monopulse system (However, they are simply referred to as a monopulse, and a monopulse radar).
FIG. 1 is an explanatory view of the configuration of the conventional monopulse radar.
In FIG. 1, a monopulse radar 1 is a simple system including a transmission antenna 11, two reception antennas (a first reception antenna 12 and a second reception antenna 13).
In this example, the first reception antenna 12 for a phase standard is set to the origin of the Cartesian coordinates (orthogonal coordinates, Descartes coordinates) (in FIG. 1, the direction of the array of the antennas is set as the X axis, and a direction orthogonal to the X axis is set as the Y axis), and the angle of the object to be detected that is measured with the clockwise on the positive Y axis set as the positive direction of an angle is θ. For simplicity, it is considered that each size of the antennas 11, 12, and 13 can be ignored with respect to the apparatus to which the monopulse radar 1 is loaded, and the geometry of each of the antennas 11, 12, and 13 is planar.
FIG. 2 is an explanatory view showing an example of a practical operation of a monopulse radar.
In FIG. 2, the monopulse radar 1 described above with reference to FIG. 1 is loaded into an own vehicle 21 such as an automobile, and detects another vehicle 22. In the state of the own vehicle 21 and the other vehicle 22, dLOS indicates the relative distance of the other vehicle 22 with respect to the own vehicle 21, ΘLOS indicates the angle clockwise from forward (Y axis direction) the own vehicle 21 to the position of the other vehicle 22, and vLOS indicates the relative velocity of the other vehicle 22 with respect to the own vehicle 21. It is assumed that the own vehicle 21 and the other vehicle 22 are moving, and the monopulse radar 1 is loaded at the forward center of the own vehicle 21.
In the above-mentioned state, the relative velocity vLOS is obtained by performing an orthogonal projection on the moving velocity v of the other vehicle 22 on the line of sight connecting the own vehicle 21 and the other vehicle 22.
For example, FIG. 2 shows the state often encountered in the actual running environment when the other vehicle 22 interrupts the own vehicle 21 in the lane. However, when the velocity (in the X axis direction) when the lane of the own vehicle 21 crosses the sane of the other vehicle 22 is calculated by the following equation (1).vLOS sin θLOS  (1)
The relative velocity vLOS cannot be determined whether it is an orthogonal projection of the moving velocity v or an orthogonal projection of another moving velocity, for example, v′, only from other two pieces of information, that is, relative distance dLOS and angle θLOS. Although it is certain that the moving velocity v is an actual velocity, the actual velocity vX of the other vehicle 22 in the X axis direction can be calculated using the moving velocity v of the other vehicle 22 and, for example, an angle α made with the X axis by the following equation (2) (check the direction of α).vx=v cos α=vLOS cos α/sin(θLOS+α)  (2)
When angle ΘLOS is not 0 (ΘLOS≠0), the observation error is defined by the following equation (3).
                                                                                          v                  ⁢                                                                          ⁢                  cos                  ⁢                                                                          ⁢                  α                                                                      v                    LOS                                    ⁢                  sin                  ⁢                                                                          ⁢                                      θ                    LOS                                                              =                                                cos                  ⁢                                                                          ⁢                  α                                                  sin                  ⁢                                                                          ⁢                                      θ                    LOS                                    ⁢                                      sin                    ⁡                                          (                                                                        θ                          LOS                                                +                        α                                            )                                                                                                                                              =                                                2                  ⁢                  cos                  ⁢                                                                          ⁢                  α                                                                      cos                    ⁢                                                                                  ⁢                    α                                    -                                      cos                    ⁡                                          (                                                                        2                          ⁢                                                      θ                            LOS                                                                          +                        α                                            )                                                                                                                                              =                              2                                  1                  -                                      cos                    ⁢                                                                                  ⁢                    2                    ⁢                                          θ                      LOS                                                        +                                      sin                    ⁢                                                                                  ⁢                    2                    ⁢                                          θ                      LOS                                        ⁢                    tan                    ⁢                                                                                  ⁢                    α                                                                                                                          =                              2                                                      2                    ⁢                                          sin                      2                                        ⁢                                          θ                      LOS                                                        +                                      2                    ⁢                    sin                    ⁢                                                                                  ⁢                                          θ                      LOS                                        ⁢                    cos                    ⁢                                                                                  ⁢                                          θ                      LOS                                        ⁢                    tan                    ⁢                                                                                  ⁢                    α                                                                                                                          =                              1                                                      sin                    2                                    ⁢                                                            θ                      LOS                                        ⁡                                          (                                              1                        +                                                  tan                          ⁢                                                                                                          ⁢                                                      α                            /                            tan                                                    ⁢                                                                                                          ⁢                                                      θ                            LOS                                                                                              )                                                                                                                              (        3        )            
It is clear that the error is exceedingly large when the angle ΘLOS→0 or α→−θLOS.
Document: Japanese Patent Application Publication No. H8-124100
In the conventional technology above, the shorter the relative distance dLOS between the own vehicle 21 and the other vehicle 22 is, the less time is allowed to the own vehicle 21 in response to the behavior of the other vehicle 22, thereby causing the danger of a clash between the own vehicle 21 and the other vehicle 22.
As a result, there is a proposition that the above-mentioned disadvantage can be overcome by using a plurality of monopulse radars 1. Although there are some examples of the apparatuses by simply using a plurality of monopulse radars 1, they are based on the angle of an object to be detected, or a distance measurement, and there are no examples based on the estimation of the actual velocity of the object to be detected.
FIG. 3 is an explanatory view of the problem occurring when two monopulse radars are used.
For simple explanation, as shown in FIG. 3, a left radar 31 and a right radar 32 are loaded on the left and right forward of the own vehicle 21. FIG. 3 shows only the actual velocity v of the other vehicle 22 as an object to be detected, the relative velocity vL between the own vehicle 21 and the other vehicle 22 measured by the left radar 31, the angle ΘL clockwise from forward (Y axis direction) of the own vehicle 21 to the position of the other vehicle 22, and the relative velocity vR and the angle ΘR measured by the right radar 32.
When the actual velocity v is obtained, it is considered that these four amounts of measurement (relative velocity vL, relative velocity vR, angle ΘL, and angle ΘR) can be combined. However, there are two serious problems only by expanding the conventional methods.
(First Problem)
When the projection (vL sin ΘL, vR sin ΘR) of the relative velocity vL and vR in the X axis direction, and the projection (vL cos ΘL, vR cos ΘR) in the Y axis direction are used, the projection of the actual velocity v in the X and Y axis directions is expressed by the following equation (4) with respect to certain linear coupling coefficients a, b, c, and d as clearly shown in FIG. 3.vX=αvL sin θL+bvR sin θR vY=cvL cos θL+dvR cos θR  (4)
However, since the linear coupling coefficients a, b, c, and dare unknown, it is necessary to estimate them by any means. In estimating the linear coupling coefficients a, b, c, and d, a large volume of data and calculation are required, and it is not practical to implement them when there are problems of quick response and a low speed calculation device.
(Second Problem)
FIG. 4 is an explanatory view showing the second problem.
As shown in FIG. 4, aside from the first problem, v and, for example, v′L are considered as candidates for the actual velocity for the relative velocity vL and the angle ΘL, and v and, for example, v′R are considered as candidates for the actual velocity for the relative velocity vR and the angle ΘR. The second problem comes from that the angle ΘL and the angle ΘR only indicate the amount of the inclination of the relative velocity vL and vR to the Y axis. To solve the problem, it is necessary to specify the relative position among the v, v′L, v′R including the actual velocity v to be obtained.
Conventionally, these first and second problems have been overlooked, and most of the techniques relating to radars are oriented to the improvement in accuracy of the measurement amount in the direction of the line of sight.
As described above, when a conventional detecting and ranging apparatus is solely used, the relative distance and the angle between an object A (the own vehicle 21 above) loaded with the detecting and ranging apparatus and the object B to be detected (the other vehicle 22 above), and the relative velocity in the direction of the line of sight between the object A and the object B to be detected can only be estimated. In addition, it has not conventionally been highly regarded that it is difficult to estimate the actual velocity of an object to be detected, and no means to solve the problem (difficulty in estimating the actual velocity of an object to be detected) have been devised.
On the other hand, it has not been an idea of estimating the actual velocity of an object to be detected although there are only a few propositions of improving the measurement accuracy in the distance, angle, or velocity in the direction of the line of sight with respect to the object B to be detected by combining a plurality of detecting and ranging apparatuses.
Although the above-mentioned detecting and ranging apparatus is used, it is very hard (for example, in processing a large volume of data) to estimate the actual velocity of an object B to be detected unless an important point is considered.